Latent Fingerprints

What Are Latent Fingerprints
May 28, 2009

In forensics, latent fingerprints are marks left at the scene of a crime which may not be immediately visible to the naked eye. The hands and feet are naturally oily, due to the *eccrine glands, which secrete sweat, a mixture of water, salts, and other trace compounds. The sweat adheres to the ridges of the finger. When a finger is placed on a surface such as glass, plastic, or wood, an impression known as a fingerprint will be left behind. The natural oils of the body preserve the fingerprint. Sometimes, latent fingerprints are made from substances other than sweat such as blood, other body fluids, or paint. ~snipped~

Part of the analysis performed on latent fingerprints includes a determination of what the fingerprint was made from. This may provide additional evidence about the criminal or the crime. One of the first things investigators do after photographing the entire scene is dust for latent fingerprints. Dusting for fingerprints ensures that no prints are missed, even if patent fingerprints, prints readily visible to the naked eye, are evident.

Specialized fingerprint powder is gently brushed over surfaces which may hold fingerprints to see if any appear. If latent fingerprints emerge after dusting, they are photographed and then carefully lifted with clear tape before being affixed to fingerprint cards. For difficult surfaces, another process known as fuming may be used to find latent fingerprints. Fuming can be used for very old fingerprints, because it causes a chemical reaction with trace substances which may be left behind by a fingerprint, even if the sweat itself is gone.

In the United States, the Integrated Automatic Fingerprint Identification System (IAFIS) is a national database of fingerprints which police investigators can use to get more information about prints found at crime scenes. The electronic database contains over 47 million records, and can be used to instantly check fingerprints from a crime scene. Fingerprint records for IAFIS come from criminals, as well as citizens who are fingerprinted as part of a routine background check.